In cellular communication systems, there is a constant and growing desire to reduce the power consumption of the so called Radio Access Network, the RAN, i.e. those parts of the system which do not include the user terminals.
A large part of the power consumption in a RAN lies in the controlling nodes of the cells in the systems, nodes which are referred to by different names in systems of different standards, but which are sometimes referred to generically as Radio Base Stations, RBS, or merely as base stations. In WCDMA systems, for example, RBSs are referred to as NodeB, and in LTE systems, RBSs are referred to as eNodeB.
However, regardless of the name and the system, a primary function of an RBS is that all traffic to and from users in a cell is routed via the RBS, which at least in part accounts for the large amounts of energy consumed by an RBS.
In LTE and WCDMA systems, the RBS also has the function of scheduling transmissions to and from the user terminals in a cell, a function which is usually performed by a so called MAC, Media Access Control, scheduler in the RBS.
Of the components in an RBS, a major power consumer is the so called Power Amplifier, the PA. Current demands for high peak data rates at the borders of the cells require the PAs in the base stations to have a high output power capability. A drawback of this is that the PA in most RBSs is overdimensioned for most normal operating scenarios, the drawback being that an overdimensioned PA consumes more energy than necessary.
A PA will have a peak output power as well as an average output power, with the difference between the two being known as the Peak-Average-Power Ratio, the PAPR. The PAPR of the PA ties into another important parameter of the transmissions from the base station, the so called Error Vector Magnitude, the EVM: in order for the transmissions from the base station to have a low EVM, the PA must be “backed off” (i.e. to reduce the output power from the peak output power) so that the sum of the average output power and the PAPR remains within the so called linear part of the PA. However, a high degree of “backing off” causes a high loss of efficiency in the PA, resulting in unnecessary energy consumption.